A model which simulates the diurnal dependence of the optical refractive index structure parameter within the atmospheric boundary layer is constructed by solving an energy balance equation for the ground surface temperature. This solution yields surface fluxes of sensible and latent heat. Empirical relationships are then used to calculate Cn2. Model results compare favorably with data obtained at a desert location under clear skies. A sensitivity analysis indicates that Cn2 is particularly sensitive to time of year, wind speed, the product of soil heat capacity and soil density, and soil moisture content. This model is applicable over relatively flat surfaces with little or no vegetation.